This invention relates to drying wet carbon black pellets by physically contacting wet carbon black pellets with carbon black smoke.
More particularly this invention relates to a process of producing dry carbon black pellets, which comprises the steps of (1) combusting a hydrocarbon feed to form a combustion product comprising carbon black particles and gaseous products, (2) quenching the combustion product of step (1) to form a carbon black smoke, (3) separating the carbon black smoke stream into at least two streams comprising stream A and stream B, both of which are at least 700xc2x0 F., (4) conveying carbon black smoke stream A through a main filter at a temperature below the upper operating limit of the filter to separate carbon black particles from by-product off gases, (5) conveying the carbon black particles from step (4) to a pelletizing area, mixing with water and pelletizing to form wet pellets, and (6) contacting the wet pellets of step 5 with stream B, which is at a temperature of at least 700xc2x0 F., to dry the carbon black pellets.
The typical furnace carbon black process utilizes a standard sequence of process equipment. Raw materials including an oxygen containing gas such as air, a fuel such as natural gas or fuel oil, feedstock oil, and potentially other additives are metered into a reactor where the feedstock oil is thermally converted to carbon black and gaseous by-products.
The reaction is stopped by cooling the reaction mass, typically by the use of water introduced into the reaction to below 2000xc2x0 F. The resulting smoke stream, which contains carbon particles less than 0.5 microns, is conveyed through a smoke header containing energy saving devices such that the combustion smoke stream enters the air preheater to cool the smoke stream to about 1000xc2x0 F., oil preheater and possibly, other devices, such as a cooling tower quench, before entering the main filter, usually a bag filter at a temperature below the upper operating limit of the filter, typically about 500xc2x0 F. The higher the smoke stream temperature, the shorter the life of the main filter.
The main filter separates the primary product carbon black from the by-product off-gases. The carbon black can be any product having nitrogen surface area ranging from 8 m2/gm to 300 m2/gm, and DBP absorption ranging from 50 cc/100 gm to 200 cc/100 gm. The off-gases that result from the combustion are high in moisture content and have a combustion value wet in the range of 50 BTU/CF to 150 BTU/cf. Sometimes these gases are combusted and the heat used in boilers for producing steam, in carbon black dryersxe2x80x94rotary dryers and fluid bed dryers, and for other purposes. In many plants, the steam produced is used through a turbine/generator set to produce electricity.
Typically, the carbon black is gathered from the main filter and conveyed, using a smoke conveyor or an air conveyor, to a pelletizing area where it is temporarily held in the fluffy and dry form in a tank. From here it is fed to a mixer where water and other pelletizing additives are introduced in measured amounts and mixed with the carbon black. The resulting mixture is mechanically formed into pellets of about 1 millimeter in diameter or 104 times the size of carbon black particles in the smoke. These wet pellets, which contain from 30% to 65% water by weight, are introduced into a dryer, either rotary or fluid bed, where the water is driven off with externally supplied heat. The gas stream containing the vaporized pelletizing water is discharged from the dryer and filtered.
Heat to the dryer for driving off the water from the wet pellets is normally supplied by combusting off-gas, natural gas or some fuel with air in a combustor. Usually this hot gas stream is circulated around the dryer drum and inside a dryer firebox and part or all of the stream is used to carry the released moisture from the dryer to a second filter.
Dried carbon black from the dryer is conveyed to bulk storage tanks using a series of equipment such as elevators, screw conveyors, belts, pneumatic conveyors, vertical or inclined drops, etc. The product normally passes through screens and magnets during the conveying from the dryer to storage. From storage, further conveying is available to reach packaging facilities.